Painton was born in Rome and raised in Paris, where she attended the Lycée de Sèvres and graduated from L'École Alsacienne. She received her B.A. in history from Mount Holyoke College in 1980. She is fluent in French.
Painton currently lives in New York City and is the mother of two children, Isabel and Anthony Smith.
Painton is the daughter of Frederick Painton and the late Patricia High Painton. Frederick was the bureau chief for U.S. News and World Report in Rome, covering Southern Europe and North Africa. He moved to Paris to be its correspondent. He stayed in Paris for about 40 years, but while there moved from U.S. News to TIME to help launch its European edition. He retired from Time as a senior writer in 1991. Patricia was a business journalist who was based in Paris for many years.
She joined Time as a correspondent for the New York bureau in 1989, specializing in writing about politics and American life. She wrote cover stories on Atlantic City, Orlando, and country music, as well as on the 1992 Man of the Year, Ted Turner, in which she revealed that he suffered from manic depression.
In 1994, Painton became Time's business editor, where she oversaw covers on everything from DreamWorks to derivatives. Later, she was appointed Nation editor, where she managed the magazine's political coverage and all of its domestic news.
As one of the only women managers at Time, she commissioned cover stories on everything from "Is Feminism Dead?" and "The Female Mid-Life Crisis" to whether kids have too much homework. But political coverage still took up most of her time: she oversaw coverage of the rise of Bill Clinton (Time's investigation of the campaign finance scandals in 1996 and 1997 won the Goldsmith Investigative Journalism Prize), the fall of Newt Gingrich, and the election and re-election of George W. Bush.
In November 2007, Painton edited a column  by Joe Klein about an amendment  to the F.I.S.A. law. Liberal bloggers Jane Hamsher and Glenn Greenwald argued that the column was inaccurate. Time later issued a clarification on Klein's column.[clarification needed]
- MHC Alumna Offers Journalism Course - Mount Holyoke College News & Events, October 31, 2006
- The Tone-Deaf Democrats - Joe Klein, Time magazine, November 21, 2007
- Corrections & Clarifications Chicago Tribune, November 29, 2007
- Time Magazine circles the wagons around Joe Klein - Jane Hamsher, FireDogLake.com, November 27, 2007
- Demand Answers from Time Magazine - Glenn Greenwald, Salon, November 27, 2007
- Painton Named E-I-C of S&S Adult Trade Publishers Weekly, January 16, 2008